Z track is great, however if you can z-track you "ass" you are a better man than me LOL. In my opinion you can either use the short 5/16 by going straight in or use the long 5/8 by inserting at a 45° angle, either way you will have the same depth in the subcutaneous layer.

Depending on how large your glutes are and whether you are using a 1.5" needle, prewarming and injecting slowly you may be just fine doing 3ml in your glute, remember nebido is usually administered as a 4 ml shot. The amount you are able to inject at one time also depends on the compound, don't ever try injecting 3 mls of Test Prop at once LOL.

The above are just my opinions and should not be taken as fact.

FFM