1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

t = int(input())

for T in range(t):
    n = int(input())
    l = list(map(int, input().split()))
    s = set(l)
    nl = list(s)
    nl.sort()
    x = -1
    # if len(nl)>=3:
    # y = nl[-1]

    y=max(l)
    for j in range(n):
                if l[j]==y:
                    if j>0 and j<n-1:
                        if l[j]>l[j-1] or l[j]>l[j+1]:
                            x = j+1
                            break

                    # if l[j]>l[j-1] and j>0:
                    #     x=j+1
                    #     break

                    if j==0 and l[j]>l[1]:
                        x = 1
                        break

                    if j==n-1 and l[j]>l[n-2]:
                        x=n
                        break



    # else:
    #     for i in range(1, n-1):
    #         if l[i]>l[i+1] and i<n-1:
    #             x = i+1
    #             break
    #
    #         if l[i]>l[i-1] and i>0:
    #             x = i + 1
    #             break





    print(x)




