Two lines subscript in summation symbol - LaTeX

The command substack in amsmath package enables summation subscripts to be multi lines.

\[
\sum_{
    \substack{
        n \in \Lambda \\
        0 < i < n
    }
} f_{n} (a_{i})
\]

\[ \sum_{ \substack{ n \in \Lambda \\ 0 \lt i \lt n } } f_{n} (a_{i}) \]

If a subscript is too long, the spacing around the sum symbol is automatically adjusted by the subscript.

\[
\sum_{
    \substack{
        n \in \Lambda \\
        0 < i < \frac{\sqrt{n}}{2} + \sin n + n^{2p}
    }
} f_{n} (a_{i})

\[ \sum_{ \substack{ n \in \Lambda \\ 0 \lt i \lt \frac{\sqrt{n}}{2} + \sin n + n^{2p} } } f_{n} (a_{i}) \]

The command \mathclap in mathtools package fixes that issue and the additional spacing between the sum and equation disappears.

\[
\sum_{
    \mathclap{
        \substack{
            n \in \Lambda \\
            0 < i < \frac{\sqrt{n}}{2} + \sin n + n^{2p}
        }
    }
} f_{n} (a_{i})
\]

\[ \sum_{ \mathclap{ \substack{ n \in \Lambda \\ 0 \lt i \lt \frac{\sqrt{n}}{2} + \sin n + n^{2p} } } } f_{n} (a_{i}) \]