Volker, I'm not sure i understand what you mean by
the (straight) sitting position
i can only imagine you mean sit straight and not particularly more leaning to one side, (is it?)
i've got to say that Geronimo prefer to lay down on his right side (i sit next to him, to his left side), and since he kind of invented this sitting thing he gets up from laying down to a sitting position while still somewhat putting more weight on his right hip, i will ask him sometimes to turn toward me while sitting with his front legs and then position himself and spread his wight a bit more equally on both hips.
this is a good question - if it is bad for hip joints,
it feel to me he will stand up just fine when he feels its time, but i cant tell.
this did grow out of his natural rising up routine, at first he would just stretch his front legs without really getting up, then he picked himself up but would just pause a little before completely leaving the ground and then it got to what it is today. i still feel it is progressing since at times it seems as if he is making an effort not to slide downwards with his front hooves, as if there is a lot of weight on the hooves and that is why he is slipping and as balanced on his hind end /core belly.
he is indeed sweet.
yesterday was the first time erez (husband) expressed interest in playing with Geronimo (Geronimo has no one but me as his human play mate and Uri is just to young to play with him on his own) obviously i encouraged it and suggested asking Geronimo to lay down with him to give them some intimacy and trusting start,
well Geronimo lay with him for a long time and then sat with him some more... woo hooo