There is no such thing as a "half level" in 4e, nor has there ever been in D&D, so I'm not quite sure what you're arguing for here.
First, I am discussing, not arguing. I'm trying to come up with an extremely simple system of making larger monsters badass without tweaking the monsters a lot.
And as I stated, half level increase XP-wise.
Add an extra half of a level of XP for a large monster that does extra damage.
Instead of 500 XP for a 10th level Standard monster, it would become 550 XP for a Large, 600 XP for a Huge, and 650 XP for a Guargantuan.
Since the monster doesn't actually gain hit points, to hit, defenses, special abilities, etc. of a higher level monster, I didn't think that each size increase rated an entire level's worth of XP.
For the most part, it is still a 10th level monster. It just happens to do more damage and hence, rates a bit more XP. It's a greater challenge.
I am puzzled. Why are you so resistant to the idea that using a monster of level + x accomplishes your goal? Are you trying to keep the hit points down? Doesn't THAT fly in the face of realism? Shouldn't a huge brute have more hps than a medium one AND do more damage? Because that is exactly what higher level means when you're talking about monsters in 4e.
Actually, higher level means more than just more hit points.
There are several reasons to not use a higher level monster. For one, they are harder to hit and have more hit points, so they drag an encounter out longer. The game is already grindy enough without doing that. Second, I still want players to experience certain types of creatures at certain levels. I don't want to throw Trolls at 3rd level PCs, just because a Troll is a larger monster. I want to throw Trolls at level 5 or 6 PCs. But when I do, I want the Troll to be badass.
A well designed 1st level Fighter does more average damage then a 10 foot tall 600 pound 7th level Cave Troll.
To me, that's just stupid. Obviously, YMMV.
I'm glad that works in other people's imaginations, but it doesn't work in mine. So, I am looking for a simple adjustment.
As a suggestion, instead just make the monster an Elite.
I was trying for a simple system.
Adding an extra dice of damage is easy to remember in game and I don't have to do a lot of extra work like add an entire template out of game. Plus, the concept works regardless of whether the monster is already an elite, a solo, a minion, or whatever.
The KISS priniciple.