[AngelicaDeAlquezar]

Podría ser que + past subjunctive => Hypothesis of something that happened in the past.

- Podría ser que Juan estuviera planeando una maldad.
It could be that Juan was planning to do something wrong.
- Podría ser que los niños tuvieran hambre.
It could be that the children were hungry.
- Podría ser que el teléfono estuviera descompuesto.
It could be that the phone was broken.


Podría ser que + present indicative => Guessing that something will happen in the future (or present, depending on the context).
- Podría ser que Juan esté planeando una maldad.
It could be that Juan is planning to do something wrong.
- Podría ser que los niños tengan hambre.
It could be that children are hungry.
- Podría ser que el teléfono esté descompuesto.
It could be that the phone is broken.


Since there is not much context of those examples with "podría ser mejor si", some sound strange, but mostly, the difference between the usage of past subjunctive and present indicative, is in how possible the speaker believes things will improve if something happens; the present indicative is for situations more likely to happen than the past subjunctive. And sometimes, it just feels more polite to use the past subjunctive, like in your saddling example than using the present indicative.

- Podría ser mejor si no montas aquí. -> This could be felt slightly rude, so the speaker prefers a more polite "si no montaras".
- Podría ser mejor si regresara otro día. -> I might come back, but it's not likely. Yet if I say "si regreso otro día", I will come back and try being more opportune.
- Podría ser mejor si vienen a vivir con nosotros. -> More like an invitation, as it is with "si vinieran", it feels rather like an imposition.