Amanvari,
I've got 2 Roths - a seedling & a larger Roth with 1 fan with 3 more fans on the way - It's swollen at the base it should be comming into bloom soon.
Anyways ... I grow them both under 4 - 48inch lights. Potted in a 50% peatmoss based media. The temps vary since I have 4 seasons. During the cooler months the tempts can range from 68 to 72, the growth is slower during this time of year. Warmer months from May to end of august the tempts will push up to 85 degrees with very high humidity.
Again, during the warmer months I drop them down further below the lighting - with the high lighting and higher tempts I've noticed there is some stress to the leaves even though they are even more moist then in the cooler months. They don't grow any less being lowerd down into the shelf a few inches, but they look better with less leaves curves or dimpling look to the leaves -- less stress.
1 thing I have noticed with Roths is that they can take a higher light then my other paphs. With my other paphs I have to take out a few tubes in the onset of summer, they just can't take the ligh and heat together. So push you're roths with higher light, they will grow faster - If there is too much yellowing then just back off a bit.
I fertilize every 2nd week - changing from a 8-7-6 to 24-8-16 -- Miracle gro.
Don't be worried that you're roth is not growing as fast as some of you're others - they are known to be kinda slow