For smaller ice, just don't fill the tray as much.
Oh heck, that's too hard
I "wanna do things the harder way".
The nice thing is you can DIY any concoction for sediment ferts you wish, soils, clays, loams, mulm, peat, osmocoat, whatever.........ADA AS also works in lieu of clay(well, it is clay) and you can pack it full of osmocoat also.
Not a bad idea for water column folks who leave for vacation for a few days.
I still like a full rich sediment bed of ADA AS or Worm castings, clay hydric soils....but if you need spot or add to existing sediments, this a good cheap simple method to DIY.
This also can help identify problems with sediment only dosing methods also(but water column + sediment dosing works best) since you can spot treat problem areas, plants with specific nutrients etc.
Over time, most sediments decline in N in planted tanks(9 to 18 months??), much less for the other nutrients though. Fish can supply some N also, but some plants demand more than others for nutrients(and CO2 for that matter).
This is simple tool to see if it's a nutrient issue.