Philebus 42b2-6

Socrates is trying to convince Protarchus of a second way in which a pleasure can be false.  This kind of false pleasure somehow arises out of a mistaken comparison with a pain in a way similar to that in which things that are closer or further away sometimes appear larger or smaller in comparison with one another than they really are.  At 42b2-6 he says:

Νῦν δέ γε αὐταὶ διὰ τὸ πόρρωθέν τε καὶ ἐγγύθεν ἑκάστοτε μεταβαλλόμεναι θεωρεῖσθαι, καὶ ἅμα τιθέμεναι παρ' ἀλλήλας, αἱ μὲν ἡδοναὶ παρὰ τὸ λυπηρὸν μείζους φαίνονται καὶ σφοδρότεραι, λῦπαι δ' αὖ διὰ τὸ παρ' ἡδονὰς τοὐναντίον ἐκείναις.

 Which I think means something like:

But now, because of the fact of being seen from nearby and then far away in turn and, at that same time, being set against one another, the pleasures appear greater and more intense when compared with pain, while the pains seem the opposite when compared with pleasures. 

I'm a bit confused by this.  On the face of it, Socrates seems to say that pleasures seem greater and more intense when compared with pain and that pains seem lesser and less intense when compared with pleasures.  But why should that be so?  I might think that what he ought to say is something about us being biased to the near, whether what is nearer is a pleasure or a pain: the nearer pleasure seems greater and more intense than it ought in comparison with a further pain and a nearer pain seems greater and more intense than it ought in comparison with a further pleasure.  But he doesn't, or at least I don't think he does.  (Damascius thinks he does: In Phileb. §187.)[1]  Socrates does not say that nearer pains appear greater and more intense than they ought in comparison with later pleasures.  But such a claim about nearer pains seems at least as plausible as the claim he certainly does make about nearer pleasures. 

Is it because Socrates thinks we are biased not to the near but to the pleasant?  This might be what be he is interested in rather than a bias to the near; the analogy with nearer and further objects of sight would on this account be rather misleading.  Or could it be that he somehow combines the two thoughts?  He thinks we are biased so as to tend to overvalue mistakenly only the nearer pleasure (but that we do not equally tend mistakenly to overvalue the nearer pain).  Or is Socrates simply not at all interested about mistakes concerning pains, only those that concern pleasures and therefore is not very careful to spell out the possibility of doloric mistakes?

[1] : Ὅτι ὡς ἐπὶ τῶν αἰσθητῶν τὰ μὲν ἐγγύθεν ὁρᾶται μείζω, τὰ δὲ πόρρωθεν ἐλάττω, τὰ αὐτὰ ὄντα, οὕτω καὶ ἐπὶ τῶν ἡδέων καὶ ἐπὶ τῶν λυπηρῶν· τὸ γὰρ παρὸν ἀεὶ μεῖζον εἶναι δοκεῖ τοῦ ἀπόντος, καὶ <λυπηρὸν> λυπηροῦ καὶ ἡδὺ ἡδέος καὶ ἡδὺ λυπηροῦ καὶ λυπηρὸν ἡδέος.