This particular concept was originated by individuals other than myself -- the idea of creating Size as a new statistic in HERO 5th Edition, instead of using powers and disadvantages to simulate things. It's not necessarily something I agree with, but once it was pointed out to me, I figured as long as they were going to do it, they should have done it right. Instead of simply one statistic, Size, I created two, Size and Density. Hell, read the changes below. Note this has not been playtested, only subject to mathematical analysis.
Size and Density as Statistics
Size and Density are the new Primary Charcteristics for this variant of HERO 5th Edition. Incidentally, both Strength and Body are now Figured Characteristics, based on the assumption that no primary attribute should figure into any other primary attribute. Both Size and Density start at level ten, like every Primary Characteristic. Both cost two character points per level. In hero tradition, Size is abbreviated "Siz" and Density is abbreviated "Den."
Every ten levels of Size doubles one's reach and height; 10 levels lower halves one's height. Every 5 levels of Size difference between two opponents gives a DCV/PER bonus of +1 to the smaller opponent, and a -1 to the larger one. Size can also add (or subtract) dice to (or from) certain types of presence attacks. Add one die per ten points of positive size differential, or subtract one die per ten points of negative size differential. Density is much simpler. Every five levels in the Density attribute doubles mass; dropping 5 levels halves it.
This quite obviously changes the Figured Characteristic chart in several ways. We assume, again, that all Figured Characteristics are their own layer, derived directly from Primary Characteristics and not each other.
Body was reduced in CP cost because of the lack of the figured characteristics it effects. Strength, however, is often cited as overpriced, so its cost remained the same. "Stunning Threshold" basically replaces the "Con Stun", and is now a variable that can be changed separately. Everything else should be pretty obvious. Oh, yes, I also believe that, with this variant, you can now be allowed to buy down as many Figured Characteristics as you want, without running into the "getting more points" problem.
I'm not entirely happy with how this turned out, and may come back to edit it later. Growth and Density Increase both affected Strength, so I had Strength affected by increases in both Size and Density - that sometimes feels silly to me. Moving Strength back to a Primary Statistic, however, might cause more problems than it solves (not the least a renegotiation of the costs of both Size and Density). So everything remains as it is, for the moment.