Transformer Tap Winding Arrangement

a two winding transformer where voltage variation is required on HV side for HV variation. in almost all the cases, for lower power ratings the tap winding is provided in the body (middle portion) of the HV winding.

My doubt is that why the tap winding is provided always on the middle of the HV winding . y not at top of the winding or bottom of the winding.

as for by my knowledge, there are two reasons for this.

1. if the tapwinding is connected at the top of the winding, the tapchanger insulation level has to increase since it is connected in line end hence the tapchanger is subjected to higher impulse stress.

2.if the tapwinding is connected at the bottom of the winding, then unnecessarily we are increasing the copper weight (weight of the leads) which are going to connected with the tapchanger which is located externally top of the tank.

other than these two reasons, if there are any other you are requested to comment on this.