ss41: Sorry to be picky, but it really is FULL elev down for both cases at start of take-off roll. True, it is achieved by different sidestick deflection.
As far as the reasons, FCTM does not help very much either:
On a normal take-off, to counteract the pitch up moment during thrust application, the PF should apply half forward (full forward in cross wind case) sidestick at the start of the take-off roll until reaching 80 kts. At this point, the input should be gradually reduced to be zero by 100 kts.
[Speculation ON:] If it were for better NWS grip the situation when more is required is not a normal TO but engine fail scenario at low speed, when aerodynamic surfaces are not yet effective. The different thrust application technique is seeimgly developed to lower the risk of surge under tailwind/crosswind. Should that happen perhaps there is benefit of having full
stick down. [Speculation: OFF]
I am pretty certain that full stick down gives full elevator down all the way until the stick is released by 80 kt. Also I am pretty certain that half stick gives full elevator down with IAS=0. What goes on with elevator between 0 and 80 kts when only half stick is applied I am not sure.
Yours,
FD (the un-real)