I'm not personally familiar with that regulatory domain.
Checking the options on my controller with the following command "show ap allowed-channels country-code SG", it looks like the allowed channels are the same for indoor vs outdoor.
Allowed Channels for Country Code "SG" Country "Singapore"
----------------------------------------------------------
PHY Type Allowed Channels
-------- ----------------
802.11g (indoor) 1 2 3 4 5 6 7 8 9 10 11 12 13
802.11a (indoor) 36 40 44 48 52 56 60 64 100 104 108 112 116 120 124 128 132 136 140 149 153 157 161 165
802.11g (outdoor) 1 2 3 4 5 6 7 8 9 10 11 12 13
802.11a (outdoor) 36 40 44 48 52 56 60 64 100 104 108 112 116 120 124 128 132 136 140 149 153 157 161 165
802.11g 40MHz (indoor) 1-5 2-6 3-7 4-8 5-9 6-10 7-11 8-12 9-13
802.11a 40MHz (indoor) 36-40 44-48 52-56 60-64 100-104 108-112 116-120 124-128 132-136 149-153 157-161
802.11g 40MHz (outdoor) 1-5 2-6 3-7 4-8 5-9 6-10 7-11 8-12 9-13
802.11a 40MHz (outdoor) 36-40 44-48 52-56 60-64 100-104 108-112 116-120 124-128 132-136 149-153 157-161
802.11a 80MHz (indoor) 36-48 52-64 100-112 116-128 149-161
802.11a 80MHz (outdoor) 36-48 52-64 100-112 116-128 149-161
802.11a 160MHz (indoor) 36-64 100-128
802.11a 160MHz (outdoor) 36-64 100-128
802.11a (DFS) 52 56 60 64 100 104 108 112 116 120 124 128 132 136 140