Might be ok on a carpeted floor (you’d have to try) but otherwise I agree with Guinnless that it should ideally be on its feet (when on a hard surface). I’m only thinking about optimal musical performance - It’s gonna spin the platter fine in any position.
Mine hardly gets warm too, even in this hot weather. Just keep an eye on it if you move it somewhere with limited ventilation.
I had a 555PS on its side for a while, dealer spoke to Naim and they said it would be fine. I put it on some metal feet. Very carefully. No scratches and sounded fine. I guess Linn would advise on your Lingo.