Fan function - not behaving as it should?

Attempts to use the Fan function in a particular way last week led to some confusion - perhaps there's an issue, or perhaps it's a gap in my understanding, so perhaps someone can advise ...

Let's say I have two rows of five moving heads :

16 - 17 - 18 - 19 - 20

11 - 12 - 13 - 14 - 15

 

As I understand it, the command 11 THRU 20 FAN {CENTER} {REPEAT} 5 ENTER should select these ten fixtures in two groups of five, each group then fanning around the centre point (13 and 18 respectively), such that moving the Pan parameter should give something like this (apologies for the extremely dodgy ASCII representation!) :

/  /  I  \  \

/  /  I  \  \

 

Am I right in my understanding of how the Fan modifiers should work? Because using the above command, what I *actually* get is this :

I  I  \  \  \

/  /  /  I  I

(i.e. the fixtures don't repeat after five units, instead forming one group of ten fixtures which then fan centered on 15/16).

 

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