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

for _ in range(int(input())):
    n=int(input())
    a=list(map(int,input().split()))
    m=max(a)
    ind = [i for i, x in enumerate(a) if x == m]
    #print(ind)
    k=len(ind)
    f=1
    for i in range(k):
        if ind[i]==0 and a[1]==m:
            f=1
        elif ind[i]==n-1 and a[-2]==m:
            f=1
        else:
            if a[ind[i]-1]<m or a[ind[i]+1]<m:
                f=0
                #print("=============")
                
                ans=ind[i]
                break
            else:
                f=1
    if f==1:
        print(-1)
    else:
        print(ans+1)
