I realise there's a very slim chance but, seriously, have you looked at raising the bath to close the gap? Foam filler is going to confront you with a labour of love. After it's swelled up out of the gap and cured, you're going to have to cut it back and clean it off the bath and the tile edges to allow the sealant to adhere to those surfaces. (Here, the use of masking tape will be a definite must!). So, rather than using an ugly coving, it might be easiest to fit a good-looking one instead.