[1.7.10]Custom mob circles round and round when size set to 1.5F

I have a custom mob and I like to make the collision map match the model size so in this case a good size would be 1.5F.  I mean for the custom entity I use setSize(1.5F, 1.0F).  This makes the width/depth of the collision box to be bigger (and this can be confirmed by pressing F3+B during game to see the bounding box).

Anyway, the problem is that when the mob attacks it now goes around and around the player really fast, and just keeps going around and around.  Note this is in a flat area of the world, so isn't a matter of having trouble navigating around blocks.  Basically the pathfinding seems to never quite get where it wants to go (the player attack target) and so keeps moving the entity.

I can of course use size 1.0F but it isn't really what I want. 2.0F seems to work better but also not what I want.  I'd like to get 1.5F (and other fractional sizes) to work.

Anyway, I looked into the navigator and path finding code briefly but couldn't see any obvious reason it would have trouble with it, although there is some math floor operations and such going on.

Anyone else experience this before?