Any diagram?  Type of boat?

From your description it certainly sounds like the middle boat took more room than was required to sail to the mark and around it.  Her claim of mark room is pretty weak unless she has a very long keel and small rudder.

Etchells I’ll do a diagram tomorrow, and I should have said that the most inside boat managed to pass the mark closely upon exit

In addition to a diagram, it'd be good to know the current strength and direction, the wave state (is the leeward mark bouncing around a lot?), and what happened to the inside boat -- did they round correctly or hit the mark or bail out of the rounding at the last moment?

Etchells!!!  6m apart at a mark?!?!?!?  I thought it was a class rule for Etchells that if you're not rubbing then you're not racing!

I find it valuable to think of it the other way around.  Room is given not taken, so rather than thinking how much room a boat can take, instead think how much room must the other boat give.
Specifically,  did the outside boat's actions prevent the inside boat from sailing to the mark and rounding it?  If the bear away was only necessary for a tactical rounding, then it was not necessary to sail to the mark and round it.

 

As the windward inside overlapped boat #2 is the give way boat with mark room is only entitled to the room required to round the mark.  He is not entitled to enough room to make a tactical rounding.

 

Definitions, Mark-RoomRule 11, On the Same Tack, OverlappedRule 14, Avoiding ContactRule 18.2(b), Mark-Room: Giving Mark-Room

International 110 664 vs. International 110 64

Mark-room is not defined to allow an inside boat without right of way to sail to a mark in a tactically desirable manner.

In this diagram, Green is a Finn, and yellow a Laser. We think that this diagram is the same as AppealUS20, and that Yelow take an excessive room to turn the L mark. We think that Y have to take a penalty. It is the right decision?

Pierre, Case's 118 , 70 , 25 answer your question directly (and are internationally applicable)

Given your diagram, it appears to me that Green was on a course at #1 and #2 to provide Yellow room at the mark (see image) with only a minor course alteration required on Green's part to provide a little more. 

To the extent that Green altered course significantly to leeward at #3 to #3.5 as drawn to avoid contact with Yellow, I'd suggest that Yellow breaks RRS 11 at #3.5 when Yellow did not alter course closer to the mark.

I agree that from @2, at least, Y is sailing way too wide of the mark.  She is not sailing within the mark-room to which she is entitled and if she breaks a rule of Section A, she is not entitled to exoneration.

I have a bit of trouble with whether Y broke rule 11.

I think it's arguable that @2, G did NOT think that she was giving Y enough  mark-room and therefore she began to bear away to give mark-room, not to avoid contact.

@3, G decides that she has given enough mark-room and hails for Y to come up.  She does NOT hail protest at this time, so seemingly, she does not think Y has broken a rule.

@5, B hails protest, so the protested incident must have occurred between @3 and @5.  During all that time boats are between 0.5 and 0.75 boat lengths apart.  Certainly @3 and @4, G could have changed course to windward and closed up on Y's lee bow..  At no time after @3 does G change course away from Y.

If Y did not break rule 10 @3, for which there is no valid protest, then I don't think Y fails to keep clear at all.

And what's G doing waving a red flag on a Finn @8?

If she's protesting Y for not keeping clear while they are tacking, I think she's bot a bit of a problem with rule 16.1.

John re: "I have a bit of trouble with whether Y broke rule 11. I think it's arguable that @2, G did NOT think that she was giving Y enough  mark-room and therefore she began to bear away to give mark-room, not to avoid contact."

I agree and with the rest of your comments.  It would have to come to the details of to what extent did Green alter course to avoid contact vs to provide a little more room .. and as you say . .if Green thought Yellow was taking too much room at 2-3 (when Yellow falls off slightly toward Green), Green should have protested then.

You need to look at the issue the other way. First question, at position 2 did Green have to alter course to avoid contact? If so then Yellow breaks rule 11. If you remove the mark it appears Yellow breaks rule 11. 2nd question, was Yellow sailing within the mark-room to which she was entitled?

Mark .. do you mean at position #3?

At position 2 Green starts altering course. At position 3 Green has altered course. 

At position 2 did Green have a genuine and reasonable apprehension of collision? If we think contact would have occurred if Green held her course at position 2 then Yellow failed to keep clear and breaks rule 11. 

Regarding Pierre's situation, it seems entirely possible to me that yellow is keeping clear the entire time. Being a doofus, but keeping clear.

Returning to the original situation, I find there is not enough facts found to render a conclusion. At minimum, I need to know the outside boat's action following "middle boat bears away hard into the outside boat". I also want to know if the ~2 boat lengths from the mark occurs "upon entering the zone", or when they are abreast of the mark, as well as the amount of overlap. It makes a big difference if they have to watch out for the inside boat's stern as it swings or not. The info given does not let me reach a conclusion, and a drawing would help significantly.