How does the EFGC flail mower position behind your tractor ?
The reference point is always the centre of your tractor, i.e. where the PTO output is.
Let us assume that your tractor is 84 cm wide from its centre to the right outer edge of the tyre (i.e. 168 cm total width), then the mulcher should extend more than this 84 cm to the right from the centre of the tractor. This allows the mulcher to mow outside the right rear wheel. This would allow you to keep some distance to e.g. a fence, bush, tree or shed with the tractor and still mow flush.
The three-point bracket can be mounted in two different positions on the mower housing. These are marked here as A1, B1, etc. and A2, B2, etc.
If the mower is to extend more than 84 cm from the centre of the tractor to the right in the example chosen here, the EFGC-135 would be too narrow (A1 = 754 mm), but with the EF-155 you could already mow 11 cm outside of the right rear wheel (A1 = 954mm). This 11 cm may not be enough because you want to mow under a fence or bush. If your tractor has enough power, you could choose the EFGC-175 (A1= 1154 mm) which can mow 31 cm outside of your tractor's rear wheel, or the EFGC-195 which can do over 50 cm.