The default way of observing four or fewer lines in the OT is to assign each spectral window to a separate baseband. Having 3 basebands in one sideband and 1 in the other is not allowed for the "Sideband Separating" (2SB) receivers used for Bands 3, 4, 5, 6, 7 and 8. When using a total of four basebands you must place all basebands in the same sideband, or two in each. This restriction does not apply to the "Double Sideband" (DSB) receivers used for Band 9 and 10.
However, you may define up to 4 spectral windows per baseband. Therefore, you can configure the spectral windows in such a way as to get around this restriction in terms of the placement of spectral windows. Note that if you decide to place multiple spectral windows within the same baseband, the correlator resources are shared between the multiple windows and they must all use the same correlator setup. For more details please see the OT documentation.