Sorry to be "that guy" but the rails of that saddle appear to be a fair distance beyond the recommended manufacturers limit.
Perhaps, you can fit it to the seat post as intended and simply spin the post in the frame by 90 degrees?
If it works for you then go ahead.
The risk might come in a lack of control when riding hard, like descending while off the saddle it is common to use the sides of the saddle against the inside of one's thighs to help control the bike.
Separately you might need to angle the nose up sufficiently to get a comfortable position on the now-leading edge
A bicycle frame is too large when any of these conditions hold:
You cannot stand over the frame, one leg on the pedal and another leg on the ground. Note some large frames may make standing a bit uncomfortable both legs on the ground. That isn't how you typically stand over the frame: usually you disconnect only one foot from the pedal.
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