B2N2,
"Physically where does the reserve fuel enter the 2&3 tank?
Close to the hydraulic/fuel heat exchangers?"
Reserve tank fuel gravity feeds via a fuel line that passes through the outboard tanks 1&4 and then through the wing rib that divides the inboard and outboard tanks. The fuel then exits through a check valve immeadiately inboard of the dividing tank rib.
The 4 hydraulic system heat exchangers are located (1 in each main tank) in the aft inboard corners of each main tank (lowest point of each tank) so this places the heat exchangers in tanks 2&3 at opposite ends of their respective tanks in relation to the reserve tank fuel transfer outlets. Hope this helps.