Forgive my opinion here, too Norman, and take with a grain of salt.... I like the horizontal layout okay, and the bed is important to preserve clean compared to the ends -- keeping that part low in the mold helps.
I think gating the sprue high up will wash sand down the ends during the pour, so I like the low gating as well.
You just basically need to feed metal into the inside corners during solidification so I'd try a bigger riser off the edge at that corner, and thicker than the upright is --maybe even a blind riser -- like a ball of styrofoam. The riser has to solidify last, so needs to be thick.
Sharp Inside corners in massive casts tend to tear like that since they solidify last, and the leg and main base tend to pull metal away from it while soft.
It helps if there's a radiuus there instead of a sharp corner, even if you machine it off afterwards.
Also a bevel on the outside corner can help.
Also the present sprue and riser look small. They should normally be larger in cross section than the largest thickness you are feeding -- which looks like the bottom of the uprights. That way they hopefully won't solidify before the corner does and can keep feeding iliquid metal.
I know just a bunch of suggestions, but some or one of them might help.
Your base does look good!
