Order of Correlative Conjunction + Preposition

All options presented are grammatical.

This issue is discussed in The Cambridge Grammar of the English Language on p1307

Linear position of both and either

The usual position for both and either is at the beginning of the first coordinate, as in all the above examples: They can, however, occur to the left of the basic position, as in [44i], or to the right, as in [44b]:

[44] i

a. This was made clear both to [the men] [and their employers].

b. He was quite taken by either my [cheek] [or cheerfulness].

c. They will either have to [reduce expenditure] [or increase their income].

ii

a.[He both overslept][and his bus was late].

b. Usually he [is either too busy to come with us] [or else has no money].

c. We must prevent rapid changes [in either the mixed liquor][or in the effluent].

The coordinates are enclosed in brackets, and the markers underlined. With placement to the left, the coordinator is separated from the first coordinate; with placement to the right (which is less common, especially with both) it occurs non-initially within it. The most frequent cases involve constructions containing a preposition, as in [44ia/iic], or a determiner, as in[44ib].

Placement in these non-basic positions is quite common, particularly with either, though usage manuals tend to regard it as stylistically undesirable. In some cases, it is the only possibility other than omission or reformulation. This is so in [44iia]: the version with both at the beginning of the first coordinate is the ungrammatical [41i] above. Similarly in [44ib] placement of either before cheek gives *my either cheek or cheerfulness, which violates constraint (a) above. Placement in non-basic position here can be avoided by repeating the determiner: either my cheek or my cheerfulness.

By virtue of their ability to occur elsewhere than before the coordinate, both and either are clearly distinct from the coordinators. Given the relationship with the NP constructions shown in [38], we analyse them as determinatives which can realise the same function as coordinators. In some cases the position ofthe determinatives matches that of modifiers in clause structure: compare It [will both solve the present problem][and may also prevent future conflict], where both follows the auxiliary verb, like the modifier in It will probably solve the present problem.