Log_buffer has no effect from 10g

I installed ORACLE SPOTLIGHT for RAC and found LOG_BUFFER was shown to occupy unusually large value, then I investigated and found fixed sga and log buffer are given a one granule size(4m) irrespective of log_buffer value.

SQL> select * from v$sgainfo;

NAME BYTES RES
-------------------------------- ---------- ---
Fixed SGA Size 1290952 No
Redo Buffers 2899968 No
Buffer Cache Size 243269632 Yes
Shared Pool Size 163577856 Yes
Large Pool Size 4194304 Yes
Java Pool Size 4194304 Yes
Streams Pool Size 0 Yes
Granule Size 4194304 No
Maximum SGA Size 419430400 No
Startup overhead in Shared Pool 37748736 No
Free SGA Memory Available 0

11 rows selected.

SQL> select (1290952+ 2899968) /1024 from dual;

(1290952+2899968)/1024
----------------------
4092.69531