What is the difference in meaning when using imperfect subjunctive vs present subjunctive?

Question

What is the difference between using present subjunctive and imperfect subjunctive?

Would you agree that the difference is that in the mind of the speaker there is a more remote chance of objectivity when choosing the imperfect subjunctive than when choosing the present subjunctive? For instance:

Ojala mis perros esten entrenados. Ojala mis perros estuvieran entrenados.

The first example paints a picture of a person picking up her dogs from the trainer. The second one, could be the case of someone who has never tried to train the dogs nor has the intention to ever try to train them.

Answer 1

Actually, the difference between:

1) Ojalá mis perros estén entrenados.

and

2) Ojalá mis perros estuvieran entrenados.

is that sentence 2) is counterfactual (my dogs are definitely NOT trained, but I wish they were), while in 1) there is a chance that they are trained (I only hope they are).