The lowbie PKers guide to distention:

I believe distention works like this: You start with a buffer for how many pks you can have without distending. This is probably 5 or 10 pks. Each time you level, a couple PKs is added to your buffer. However, your buffer of PKs cannot exceed a certain size (35?). This means that, although you can have 100 PKs at level 35 without distending, you cannot level to 35 with no PKs, and then PK 100 people and expect not to distend.

When you distend, your range seems to extend upwards faster than it is reduced downwards. So distending can actually be a very nice thing as it gives you more people in range. But sometimes it becomes too much... But don't worry, just level up and your pk range will return to normal.

Getting out of distention is easy - just level up and it will go away.

Extrapolated numbers for how many PKs you can have at each level without distending:

11 10
12 12
13 14
14 16
15 19
16 22
17 25
18 28
19 31
20 34
21 37
22 40
23 43
24 46
25 60
26 64
27 68
28 72
29 76
30 80
31 84
32 88
33 92
34 96
35 101
36 106
37 111
38 116
39 121
40 126
41 131
42 136
43 141
44 146
45 152
46 158
47 164
48 170
49 176
50 182