Power Query nested if evaluation order

Hi,
I have a question re the order of using nested if's in PQ,

I want to make 'numbers" = 1000 and text strings thant start with 'a' = "AAA , if first tried this,

Does not work;

 Table.ReplaceValue( Source, "", "" , (x,y,z)=> 
                      if Text.Start(x,1) = "a" then "AAA" else 
                       if Value.Type(x) = type number then 10000 else x , 
                             Cols )

The first if does but I get an error for numbers, so I changed the order and this works

Works;

Table.ReplaceValue( Source, "", "", (x,y,z)=> 
                       if Value.Type(x) = type number then 10000  else 
                         if Text.Start( x,1) = "a" then "AAA" else x , 
                             Cols )

I can't see why they outcome should differ? I have tried by putting an if to text if it is text before taking the first value but still no good,

Table.ReplaceValue( Source, "", "" , 
                                               (x,y,z)=> 
                                                        if Value.Type(x) = type text then if Text.Start(x,1)= "a" then "AAA" else
                                                          if Value.Type(x) = type number then 1000 else x else x ,
                                                               Cols )

Can someone point out the evaluation order ?

Richard.