The block size is the default view size for radare. All commands will work with this constraint, but you can always temporally change the block size just giving a numeric argument to the print commands for example (px 20)
[0xB7F9D810]> b?
Usage: b[f] [arg]
b display current block size
b+3 increase blocksize by 3
b-16 decrement blocksize by 3
b 33 set block size to 33
b eip+4 numeric argument can be an expression
bf foo set block size to flag size
bm 1M set max block size
The b command is used to change the block size:
[0x00000000]> b 0x100 ; block size = 0x100
[0x00000000]> b +16 ; ... = 0x110
[0x00000000]> b -32 ; ... = 0xf0
The bf command is used to change the block size to the one specified by a flag. For example in symbols, the block size of the flag represents the size of the function.
[0x00000000]> bf sym.main ; block size = sizeof(sym.main)
[0x00000000]> pd @ sym.main ; disassemble sym.main
...
You can perform these two operations in a single one (pdf):
[0x00000000]> pdf @ sym.main