# How to interpret methylation calls from Bismark on opposite strands?

I'm looking at Reduced representation bisulfite sequencing (RRBS) data from ENCODE, and to align the FASTQ files I've used Bismark with Bowtie 1. When I load the resulting BAM file into R with Rsamtools and GenomicRanges, I get something like this:

> reads
GRanges object with 2 ranges and 5 metadata columns:
seqnames         ranges strand |                     seq                                   XM          XR          XG        NM
<Rle>      <IRanges>  <Rle> |          <DNAStringSet>                          <character> <character> <character> <integer>
[1]     chrM [16523, 16558]      - | ATAAAACCTA...CCCTTAAATA .....h........h.......z.............          CT          GA         3
[2]     chrM [16524, 16559]      + | TAAAGTTTAA...TTTTAAATAA .....hh.......hhh.h.z...hhhh........          CT          CT        11
-------
seqinfo: 25 sequences from an unspecified genome


For the read on the - strand (which is aligned to the "G->A"-converted reference), how should I compare methylation calls to those on the + strand, since they don't line up?

For example, the z in the methylation string of the - strand is one position ahead of the z in the + strand (which makes sense because of symmetric CpG methylation). But how should I determine whether these two methylation calls are "essentially the same" or not?