Imo I wouldnt worry about it, all 3 of the dwarf cory species are much more mid water fish than other corys, yes they do feed off the bottom but ireally wouldn't worry to much, topping the gravel with the sand will work in the short term but it will soon start migrating under the gravel
Im leaning towards using a mesh for the reason troi stated, I will probably be moving plants around alot to start with
Is this mesh suitable ?
1.2m Gardman Greenhouse Shade Net Shading Material - By The Metre / Off The Roll | eBay
I picked up a bag of fluval stratum, having never used soil substrates before I was a bit worried about how it would hold plants as it seems very light but its been superb now plants lifting at all even with my clumsy hands wafting them during water changes, although quite expensive I would...