What is the reason, or what might cause, the projected image of a negative to be less sharp on a (hand-made) 4x5 diffusion enlarger than on a Gnome Universal Alpha II 6x9 condenser enlarger? The same enlarger lens was used in both cases.

The 4x5 projected image, though appearing bright and sharp seems to be very soft(???) compared with the sharp and hard image of a projected image from the 6x9 condenser enlarger.

The prototype diffusion 4x5 enlarger was made by cannibalizing an old 6x9 enlarger.
The 6x9 support for the [old] lamp assembly has been cut back to allow 4x5 projection. The lens holder fastened to the same 6x9 support remains, though the top section of the bellows disconnected.
The negative carrier is a piece of wood fastened on top of the modified 6x9 support [for the lamp assembly] using existing screws.
The existing bellows have been extended to cover 4x5.
The lamp housing is a substantial closed card box and the 60w incandescent bulb fitted at 90 degrees to the optical axis of the lens. A rectangular opening slightly bigger that 4x5 has been cut into the lamp housing and the interior of the lamp housing is covered with silver (cooking) foil.
The negative is held between a sheet of opal glass plate and a sheet of clear glass. This sandwich rests onto top of the wooden negative carrier; and the lamp housing fits on top.
By spirit level, the negative carrier is parallel to the enlarger’s base board; and is at right angles to the enlarger’s column.

Any and all comments welcome
Regards
Tony