im not a big supporter of RAW, but you'll have trouble convincing a knowledgable opponent when it comes to the "always placed" part of the rule. common sense to me says that if the unit is 6 wide and youve got 6 kroxigors, they should adjust their position in the unit (i.e. be placed in the 3rd rank) instead of the unit adjusting its frontage to allow all the kroxigors to be placed in the 2nd rank. if only it said "when possible" in there, like all of the mandatory placement rules for command and character models within a unit.
as for the supporting attacks and rank situation, this is the way i would work it:
Scenario 1:
s s s s s s s s s s
kk kk kk kk kk
kk kk kk kk kk
kk kk kk kk kk
kk kk kk kk kk
s s s s s s s s s s s
in this example the 2x2 k's represent 1 kroxigor, for a total of 10 kroxigors in this unit. the unit is a horde (10 wide). for the purposes of ranks, there is currently 1st rank skinks, 2nd rank kroxigor, 3rd rank kroxigor, 4th rank skink. to me, that means you will have the first rank of skinks attacking plus the 2 ranks of kroxigors (front rank, supporting rank, horde supporting rank). for rank bonuses, according to our rulebook each kroxigor should be represented as 4 skinks for the purposes of rank bonus calculations. so currently that formation has 6 ranks, so would get the full +3
Scenario 2:
s s s s s s s s s s
s s kk kk kk s s
s s kk kk kk s s
s s kk kk kk s s
s s kk kk kk s s
s s s s s s s s s s s
in this example, your rank bonus would still be +3 because you have 6 ranks. what is attacking would change however. you now have 1st rank skinks, 2nd rank skinks/krox, 3rd rank skinks/krox. so you would have a total of 16 skinks and 3 kroxigors attacking since the other 3 kroxigors are in the 4th/5th ranks.
Scenario 3:
config 1
s s s s s s s s s s
s s kk kk kk s s
kk kk kk kk kk
kk kk kk
kk
or
config 2
s s s s s s s s s s
s s kk kk kk s s
kk kk kk
kk kk kk
kk kk kk
in this example, youve lost a bunch of skinks (typical). here in lies the problem with multiple ranks of kroxigors. i believe the correct way to do it would be config 1, though it doesn't LOOK right. (i.e. 3 different rank sizes). config 2 doesn't LOOK right either but my assumption is you always fill in ranks as they are depleted. this is all based on the fact you think the unit config should dictate where the models go instead of the models altering the unit config because of how many there are. truely a unique issue to lizardmen (i think

). i could go either way really, both sides have some solid arguments.