DS2 Walker size restrictions

I was wondering what the rationale was for the combat walker size
restriction of 4 and 5?  I'm developing a Battletech-esque conversion
for
Dirtside and am planning on breaking this restriction (having size 1-5,
where 1 are infantry walkers, 2 light mech,...5 assault). Am I going to
ruin a play balance issue? I do understand the walkers being 1 signature
larger (will require all mechs to buy Stealth-1 and no larger).

Note that I'm also planning on breaking other parts of the rules, like
the
armor/size restriction and adding a level of FireCon. Will share with
the
list (and possibly design a webpage) when it's ready and playtested.

--Billiam